Kinetic Study on Nucleophilic Substitution Reaction of 5-Nitro-8-quinolyl Benzoate, Picolinate, Nicotinate and Isonicotinate with Alkali Metal Ethoxide: Effect of Nonleaving Group on Reactivity and Transition State Structure 


Vol. 35,  No. 6, pp. 1789-1793, Jun.  2014
10.5012/bkcs.2014.35.6.1789


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  Abstract

Pseudo-first-order rate constants (kobsd) have been measured spectrophotometrically for the reactions of 5-nitro- 8-quinolyl nicotinate (4) and 5-nitro-8-quinolyl isonicotinate (5) with alkali metal ethoxides (EtOM; M = K, Na and Li) in anhydrous ethanol at 25.0 ± 0.1 oC. The plots of kobsd vs. [EtOM] curve slightly upward for the reactions with EtOK and EtONa but are linear for the reactions with EtOLi and for those with EtOK in the presence of 18-crown-6-ether. Dissection of kobsd into kEtO− and kEtOM (i.e., the second-order rate constants for the reactions with the dissociated EtO– and ion-paired EtOM, respectively) has revealed that the reactivity increases in the order EtO– ≈ EtOLi < EtOK < EtONa for the reactions of 4 and EtOLi < EtO– < EtOK < EtONa for the reactions of 5. Comparison of the kinetic results for the reactions of 4 and 5 with those reported previously for the corresponding reactions of 5-nitro-8-quinolyl benzoate (2) and picolinate (3) has revealed that the esters possessing a pyridine ring (i.e., 3-5) are significantly more reactive than the benzoate ester 2 due to the presence of the electronegative N atom (e.g., 2 << 3 < 4 < 5). It has been concluded that M+ ion catalyzes the reactions of 3-5 by increasing the electrophilicity of the reaction center through a five-membered cyclic transition state (TS) for the reaction of 3 and via a four-membered cyclic TS for the reactions of 4 and 5.

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  Cite this article

[IEEE Style]

J. Lee, M. Kim, I. Um, "Kinetic Study on Nucleophilic Substitution Reaction of 5-Nitro-8-quinolyl Benzoate, Picolinate, Nicotinate and Isonicotinate with Alkali Metal Ethoxide: Effect of Nonleaving Group on Reactivity and Transition State Structure," Bulletin of the Korean Chemical Society, vol. 35, no. 6, pp. 1789-1793, 2014. DOI: 10.5012/bkcs.2014.35.6.1789.

[ACM Style]

Jieun Lee, Min-Young Kim, and Ik-Hwan Um. 2014. Kinetic Study on Nucleophilic Substitution Reaction of 5-Nitro-8-quinolyl Benzoate, Picolinate, Nicotinate and Isonicotinate with Alkali Metal Ethoxide: Effect of Nonleaving Group on Reactivity and Transition State Structure. Bulletin of the Korean Chemical Society, 35, 6, (2014), 1789-1793. DOI: 10.5012/bkcs.2014.35.6.1789.

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ISSN(Print) 0253-2964
ISSN(Online) 1229-5949